How would -- feel about running a five K race on -- sweltering summer day having stuff thrown at you from all directions. -- paying for the privilege. If you -- think that sounds like a lot of fun. Yet ready for a colorful surprise it's steamy it's sweaty it's the hottest party around here's ABC's Lindsay chance. At the beginning of every race there are two possible -- victory. Or crushing defeat and on this sweltering summer day. I have a lots of competition. Life 1000 athletes ready to give it their all people like making sure there were about to find out has a lot to prove. The -- and get properly limber enough that countdown begins. And -- off but I'm not nervous because fortunately today there's a third possible outcome in this -- and getting down. Beyond recognition. This is the Brooklyn -- -- Five kilometers up on time -- bridled when revelry. A white T shirt wearing participants get bomb sprayed and -- -- died cornstarch. All in the name none and charity or victory but sheer joy. -- entry fees of around thirty to fifty dollars there. Literally paying for the privilege to get -- and his. What would happen if I got into the starting -- Of course -- case you -- them colors and had a party afterwards and party debut. Founder and master of ceremonies Travis Snider says he'd just had a hunch I think people who live -- break at your job you can. Don't worry about the mom -- the guidance. That hunch was right on point the business registered 600000. Runners at more than sixty events in 49 cities last year. This year there will be around a hundred events with a million participants. That's tens of millions of dollars. Plus there are sponsors like Chevrolet lining up for a piece of the action. The color run is the leading the pack of so called fun -- -- -- not seen anything but fun. Including the -- race were runners jump over fire. And under barbed wire -- way to do it again. Mother -- participant battle obstacles including electric -- it's. And -- -- mud runway here chased by the running dead. There are now more than 30005. -- to choose from in the US alone. And is a powerful force driving their popularity. Social media and unexpected gold mine -- free publicity. With participants desperate for the perfect profile -- The companies behind are milking it for all -- to work creating photo -- and encouraging runners and stick ran away. Into the viral nature of social media and the images of the color and -- pretty powerful. It's made it brokered for. In fact the color -- -- so popular they bought out the entire country of white T -- -- are -- -- it started with. -- that there's no more white pieces. Snyder says fun and accessibility. How about an event like the -- and does amazing things are recruiting. Come and participate. In an athletic event. 8% of color runners are hi Kate Burgess. And then there are people like my running buddy Megan please come to Brooklyn to celebrate the one year anniversary of open heart surgery. -- doctors had discovered a heart defect that -- -- the birth and operated immediately. Yeah. Now after months of therapy she's determined to kill her goal of winning a five -- But will have the stamina. May not setting any speed records that -- an -- getting it done and finally we crossed the finish line. -- may be tired but she's on top of the world. Yet it's silly thing like where's your neck yeah. I can't run I paid -- do anything up now. And it's clear that thousands of other people here feel pretty good too. For Nightline I'm -- Janet.

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